2022 Spring Student Research Symposium Oral Presentation Materials
Permanent URI for this collectionhttps://hdl.handle.net/1969.6/90412
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Browsing 2022 Spring Student Research Symposium Oral Presentation Materials by Subject "amino acids"
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Item Intramolecular N isotope analysis of glutamine in phytoplankton(2022-04) Schiereck, Samantha; Lee, Charlotte; Mnich, Alanna; Baca, Jesus; Shaw, Catherine; McMullan, Esme; Mcallister, Marysa; Tran, Dat; Altabet, Mark; Zhang, LinGlutamine (Gln) and glutamic acid (Glu) provide the first step of incorporating inorganic nitrogen (N) into cellular organic N in photoautotrophic primary producers. Both are present at higher concentrations than other amino acids (AAs). The N atom in cellular ammonia forms the amide group of Gln, which is subse- quently used in producing Glu. Although Glu supplies the N for most other amino acids via transamination reaction, Gln and Glu interconvert with each other via -ketoglutarate. We hypothesize that the 15N of Gln’s amino-N ( 15NGln-amino), amide N ( 15NGln-amide), and intracellular ammonium have the same values under equilibrium conditions due to fast turnover. In addition, the amide-N of Gln provides N for the nucleobases and one of the sidechain N atoms in histidine. Thus, position-specific N isotope analysis of Gln will provide key information on AA and nucleotide biosynthesis in organisms. To analyze the amino and amide N’s, intracellular Gln was extracted from lysed phytoplankton cells, separated, and collected by Ion-exchange Chromatography, then divided into two fractions. One sub-fraction was oxidized by hypochlo-rite, converting the amino-N to nitrite. All the nitrogen in the second fraction were oxidized to nitrate using persulfate with UV radiation. The nitrite or nitrate produced in the two sub-fractions will then be converted to nitrous oxide and analyzed using Purge-and-Trap Isotope Ratio Mass Spectrometry, yielding both 15NGln-amino and 15NGln-total. Using the mass balance, we then can calculate the 15NGln-amide by subtracting the 15NGln-amino from 15NGln-total. We will compare the 15NGln-amino and 15NGln-total with the 15N of intracellular ammonium in cultured phytoplankton to verify our hypothesis. This study will shed light on the 15N patterns of Gln and other amino acids in different phytoplankton phylogenetic groups under various metabolic conditions, which will further advance the use of 15N-AA patterns in trophic ecology and paleo-N cycle reconstructions.Item Sinking/suspended particles and zooplankton interactions in eastern tropical north pacific oxygen deficient zone revealed by δ15n-amino acids(2022-04) Lee, Charlotte; Mnich, Alanna; Catala, Fernando Contreras; García de León, Francisco Javier; Sánchez-Velasco, Laura; Baca, Jesus; McMullan, Esme; Mcallister, Marysa; Tran, Dat; Shaws, Catherine; Altabet, Mark; Zhang, LinPhotosynthesis by phytoplankton at the surface ocean fixes atmospheric carbon dioxide into organic matters that sink to the deep ocean in the form of particles. The composition and flux of particles could be affected by microbial degradation and consumption and repackaging by zooplankton. Within the oxygen deficient zones (ODZs), the zooplankton abundance is greatly reduced and oxygen is absent as electron acceptors for aerobic degradation of organic matters. Elevated biomass of zooplankton was found just below the lower ODZ boundary, presumably due to the higher availability of sinking particles for feeding. However, there is a lack of observations that could establish the link between sinking/suspended particles and zooplankton in the ODZs. A better understanding of sinking/suspended particles and zooplankton dynamics through ODZs is essential for evaluating the carbon export to the deep ocean, as ODZ is expected to expand due to the current warming climate. Sinking/suspended particles and zooplankton samples were collected at the eastern tropical north Pacific ODZ (14N, 104W) at various depths in December 2020. 15N of phenylalanine ( 15NPhe) and glutamic acid ( 15NGlu), the canonical source and trophic amino acid, are analyzed to assess the N isotope baseline and trophic positions (TPGlu-Phe) of these samples. 15NPhe and 15NGlu of surface suspended particles were 3.50‰ and 10.57‰ respectively, yielding a TPGlu-Phe of 1.48 that indicates the input of both phytoplankton and zooplankton materials to the suspended particle pool. Little enrichment in 15N of Glu was found between the suspended particles collected from the surface and below the lower boundary of ODZ (~1‰). This suggests limited trophic processing of sinking particles through the ODZ before zooplankton disaggregates them into suspended particles below the ODZ, which is in agreement with the slower sinking flux attenuation rate previously observed in ODZs.